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How to Use Pool Shock to Purify Water

Avatar for Jodie Weston Jodie Weston  |  Updated: October 20, 2020
How to Use Pool Shock to Purify Water

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If I were to ask how many of you store liquid bleach along with your other prepping supplies, I am certain that a good percentage of you would raise your hands.  Liquid bleach is a powerful disinfectant and sanitizer but did you know that there is something better?  Something with an almost indefinite shelf life that is inexpensive and takes almost no room to store?

That something is the chemical Calcium Hypochlorite most commonly known as Pool Shock.

How to Use Pool Shock to Purify Water - Backdoor Survival

I have known about Pool Shock for years but because it is not readily available in my area, I never took the time to search it out so I could stockpile some for my own emergency preps.  That has now changed and today I plan to show you how to use Pool Shock the easy way, step by step.

Why Not Bleach?

Before we start, you may be asking “why not use liquid chlorine bleach?”.  There are a few problems with liquid household bleach.  It takes a lot of room to store bleach plus the usable shelf life is only six months to a year depending on storage conditions.

The folks at Clorox say this:

The active ingredient in liquid bleach, sodium hypochlorite, is very sensitive to high heat and freezing, but under normal home storage conditions, it should still perform well for nine to twelve months.

In addition to limited shelf life, there is another problem. I have had reports from Backdoor Survival readers telling me that in their area, they can only purchase “Clorox Ultra” which is concentrated.  When I called Clorox to ask how to use concentrated bleach to purify water, they said that it was not intended to be used in that manner and why would I want to do that anyway.  Seriously, their representative actually said that.

Pool Shock – The Boilerplate

When I started doing research for this article, I visited some of the most respected survival and preparedness blogs and forums for background material.  After all, pool shock is pool shock and there must be some standards for use, right?

With just one exception, all of the sites I visited included this boilerplate from the EPA:

You can use granular calcium hypochlorite to disinfect water.

Add and dissolve one heaping teaspoon of high-test granular calcium hypochlorite (approximately ¼ ounce) for each two gallons of water, or 5 milliliters (approximately 7 grams) per 7.5 liters of water.

The mixture will produce a stock chlorine solution of approximately 500 milligrams per liter, since the calcium hypochlorite has available chlorine equal to 70 percent of its weight.

To disinfect water, add the chlorine solution in the ratio of one part of chlorine solution to each 100 parts of water to be treated. This is roughly equal to adding 1 pint (16 ounces) of stock chlorine to each 12.5 gallons of water or (approximately ½ liter to 50 liters of water) to be disinfected.

To remove any objectionable chlorine odor, aerate the disinfected water by pouring it back and forth from one clean container to another.

Have your eyes glazed over yet?  Mine have. Being an accountant, I like to deal in absolutes so what is this business about “one heaping teaspoon”?  Plus, what’s up with the references to “approximately” and “roughly”?

I decided that it was time to do my own testing, and sure enough, each time I measured out a heaping teaspoon, I had different results; they ran the gamut from 1 1/4 teaspoons to 2 teaspoons.  This made my head hurt.

Another thing.  Over and over I read that you should use pool shock that is a minimum of 78% calcium hypochlorite with the balance being inert ingredients.  Fair enough, but there are two problems with this. First, what you find locally maybe 68%, it may be 78%, or it may be something else.   Second, the EPA makes no such recommendation or at least none that I could find. They simply say “high-test”.

Did I mention this made my head hurt?

But there is more.  I actually found a couple of sites that said to use one heaping tablespoon of Pool Shock for every two gallons of water!  You know, just because you find something on the internet does not mean it is true.

My conclusion?  The exact amount and the exact percentage does not matter as long as it is within a reasonable range and close to the EPA standard.  I do think it is important that the pool shock does not contain other additives that may or may not be safe even when highly diluted.  Other than that, however, it is my belief that the precise percentage of Calcium Hypochlorite to inert ingredients does not matter as long as it is 68% or higher.

For my own use, I settled on 1 teaspoon of pool shock per gallon of water when making up my stock chlorine solution. Then, to disinfect water, I used 3/4 ounce of my pool shock solution to treat a gallon of water.  This makes it easy to calculate how much to use for water disinfection, regardless of the size of your container.

Step-by-Step: How to Purify Water Using Pool Shock

The first thing I did was to gather my supplies.  Notice that I used eye protection goggles and rubber gloves.  Other supplies included an empty bleach bottle, funnel, shot glass, and measuring spoons.

How to Use Pool Shock to Purify Water - Backdoor Survival

I verified the size of my stock chlorine solution container, namely a repurposed bleach bottle.  My bottle held 1.42 gallons and I wrote this on the outside with a Sharpie pen.  My intent, however, was to only prepare 1 gallon of stock solution to keep the math simple.

How to Use Pool Shock to Purify Water - Backdoor Survival

After donning my protection gear, I added water to my stock solution bottle, carefully measuring the quantity.  I used exactly one gallon of water.

How to Use Pool Shock to Purify Water - Backdoor Survival

I then measured out some pool shock; one level teaspoon to be exact.  I put the cap back on the bottle and swished it around a bit. I gave it a sniff test and it definitely smelled bleach-like.

How to Use Pool Shock to Purify Water - Backdoor Survival

The next step was to purify water.  I wanted to make drinking water and for me, the smaller the jug the better.  I chose a 64 ounce repurposed apple juice jug.  Remember the easy math?  The EPA says 1 part chlorine solution to 100 parts water so the math is 64/100 = .64 ounces.

Keeping things easy, that translates into approximately 2/3rd ounce.  Remember, the EPA guideline uses the word “approximately” all over the place.  That was good enough for me.  To easily measure the proper dilution, I used a mini shot glass that had measurement markings along the side.

How to Use Pool Shock to Purify Water - Backdoor Survival

Be sure to pour your pool shock into your water and not the other way around.  The last thing you want is to splash the solution on yourself on the surrounding surfaces (although you have probably noticed that I did this outdoors).

After preparing my newly purified drinking water, I drank up.  Three things.  I did not throw up, I did not get diarrhea and I did not get sick or die.

I am comfortable with the results even though the solution I made may have been slightly stronger than the EPA guidelines.  Then again, given the vagueness of the EPA guidelines, perhaps my measurements were spot on.

How to Use Pool Shock to Purify Water - Backdoor Survival

Note:  I did not find that my water had an objectionable smell or taste.  True, it was not sweet tasting like the water coming out of my Royal Berkey but it was palatable.  If your own purified water has an unpleasant odor, simply aerate it by pouring it back and forth between clean containers.  This trick applies to any water, not just water treated with pool shock.

How to Use Pool Shock to Purify Water - Backdoor Survival

Label your pool shock solution.  This is powerful stuff.  Get out your Sharpie and label the jug with as much information as you can.  Store it, in the same manner, you store liquid bleach, up high and away from pets and children and in a location that is cool, dark and dry.

Also, store your unused pool shock safely.  Because it is corrosive, I chose a mason jar with a plastic lid.  Plus, rather than empty the pool shock into the jar, I sealed the plastic bag it came in with a clip and stuffed the bag inside of the jar.

Other Handling and Storage Considerations

I contacted the manufacturer of the pool shock I purchased and requested a Material Safety Data Sheet on the product.  They promptly responded and here is what it said about handling and storage:

Keep product tightly sealed in original containers. Store product in a cool, dry, well-ventilated area. Store away from combustible or flammable products. Keep product packaging clean and free of all contamination, including, e.g. other pool treatment products, acids, organic materials, nitrogen-containing compounds, dry powder fire extinguishers (containing mono-ammonium phosphate), oxidizers, all corrosive liquids, flammable or combustible materials, etc.

Do not store product where the average daily temperature exceeds 95° F. Storage above this temperature may result in rapid decomposition, evolution of chlorine gas and heat sufficient to ignite combustible products.


Now that I have been through the process and understand the math, I am comfortable using pool shock to purify water for drinking, hygiene, and sanitation purposes.  It is not, however, an excuse for not storing water nor an excuse for not having a supply of traditional water purification liquids or tabs that are pre-measured and simple to carry with you in bug-out-bags and emergency kits.

As far as I am concerned, the pool shock I have purchased is reserved for dire emergency use, period.  Yes, I feel it is safe, but it is still a powerful chemical solution as is liquid bleach.  I will use it as the water purification method of last resort and if the time comes, I will be thankful I have it on hand.


I have to say this: I am not a chemist and I am not an expert.  My methods are my own and they work for me.  That being said, if you have any hesitation at all, visit other resources including the EPA and make the decision to use pool shock your own and not just something someone told you to do.  Here is a link:  Emergency Disinfection of Drinking Water.

The Final Word

Everywhere you look you will see a recommendation to store bleach for water purification. I have made that recommendation and so have many, if not most, of my blogging peers.  What you may not have seen is that liquid bleach has a limited shelf life of 6 to 12 months.  I fear that this could be leaving a lot of people ill-prepared to produce safe, potable water in an emergency.

This means that a person that began prepping a year ago, and does not know to rotate their bleach, is already living with false security when it comes to water purification.  And what about people that have been prepping longer?

As long as pool shock is stored properly, it will have an almost indefinite shelf life plus, a small one-pound package will treat many thousands of gallons of water. Ten thousand to be exact.  It can be mixed and used as potable water and as a disinfectant, just like bottled liquid bleach. So if you have a water storage tank and need something for emergency water disinfection, a hypochlorite solution could work out well for you.

At the end of the day, do your own research and decide for yourself.

Enjoy your next adventure through common sense and thoughtful preparation!

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88 Responses to “How to Use Pool Shock to Purify Water”

  1. History Note: a long time ago in Europe they drank ale and wine because they knew that the water would make them sick(it was always dirty}…// while building the railroad across the United States, the Chinese were much more productive than the Irish because they drank tea made with boiled water whereas the Irish drank the{dirty} water and used liquor alot and were therefore sick alot…// we actually CAN learn from history even if we are somehow doomed to repeat it………

  2. Can pool shock be used as a disinfectant and sanitizer to kill covid-19 virus? The CDC says that a 1:10 solution of regular Clorox bleach will do the trick. Can a solution made from pool shock do the same? I note that pool shock is calcium hypochlorite and Clorox is sodium hypochlorite (from the Clorox website). What difference calcium vs. sodium for this purpose?

    • You have to do the calculation, how much chlorine in the pool shock (between ~30 & 50%) and how much chlorine in the bleach being referenced? Don’t lose site of the fact that depending on your source, bleach degenerates (loses it’s chlorine) up to 50% in 6 months. Memory gives me a 5% for fresh bleach. Most recipes for pool shock end up with a volume (5 gal) of bleach that is then used as bleach.

      If you have 5% in bleach and they say a 1:10 dilution will disinfect for the virus why do you need a 90% alcohol for homemade hand sanitizer?

  3. Thanks for the vote of confidence but I still have the insecurity with how long the Pool shock will last. The pool shock is in a constant state of moving to the lowest free energy (degenerating) which is why I was so concerned about finding the correct plastic to hold it in a cool, ventilated environment. But that doesn’t answer the bigger question, is Chlorine and the filter capability of a Berkeley up to the challenge of stopping a virus. Viruses are very small and until infecting an organism, not really alive??????? Can Chlorine kill an inactive virus?

  4. Thanks for the info, especially the ratios. With this Wuhan virus, I’m spending the weekend taking stock and updating my preps. I wrote exactly what you wrote on my bucket that I’m storing the shock in. If this thing were to get serious, and water becomes an issue because of a quarantine, and no power etc, my plan is to treat all water we use with the pool shock solution, and from that, any water that is consumed, to run through our Berkey.

  5. Why oh! why can I not print this? I did a Ctrl-P and got 2 pages and nothing in those 2 pages.

  6. Has anyone offered an acceptable means of storing CH for the long term. I have put the plastic bags of CH into repurposed vitamin bottles of the proper grade plastic and put these bottles into a 5 gal plastic bucket with the best selling lid I have and this is stored in the garage. The garage gets warmer than I would like but it is the only storage spot in my house that has any real ventilation.
    To me the prepper movement has two categories, the first month and the first two years. A recent bought bleach bottle will cover the near term but long term water purification would be another issue. And, like I have said in the last I am a lazy prepper, I hate to rotate stock and love 5 gal buckets of properly stored wheat.
    I would love to hear other peoples ideas on how they have stored HCH.

  7. The issue of CH (Pure pool shock) as a water purifier has been kicked around for some time. Few thought I want to share with all:
    Longterm storage of CH is a challenge. The manufacture recommendations is cool, dark (out of any direct light) and well ventilated. Cool and dark is the basement but never truly ventilated? The storage of CH crystals is of concern because the CH decomposes to Chlorine gas. This is not nice stuff. I tried to put in in a kerr canning jar and in 6 mo to a year the metal ring was rusting on the outside. Cl gas is aggressive to most materials including plastic. I suggest you check your plastic lid and see if it hasn’t gotten quite brittle? And past article talked of an apartment deweling individual with limited storage space put can good and CH in the same confined closet and found all his cans quite rusty and the cardboard box falling apart. Storage of the crystals needs to be better thought through. I don’t have the answer.
    Use the cleanest / filtered water you can get. I have read that CH will kill girdia but was questionable about the dormant pods but they are larger than the critter.
    Also, when you start worrying about the bulk solution or the water being purified relax. Did you have to take swimming lessons at an indoor pool as a kid? Ever have an early lesson? Smell the chlorine in the pool room? That was most likely on the high side but since you are reading this not fatal. Add your CH solution to your to be drinking water, mix shake well, leave set for as long as you can, 30 to 40 min and then smell it. If you don’t smell the pool smell add more solution and do it again. If you do smell the pool smell begin to vent it off by pouring from on container to another and then drink. The pool chemistry test kit is a good idea but all the reagents in it have a shelf life. I am a lazy prepper. That is why I like CH, small volume, long shelf life, simple testing – your nose.

    • Addition to above:
      I spoke to a chemist at a plant that makes CH (Pool shock) and his comment was that the manufacturing process consists of converting Chlorine from various salts to CH. The inert portion is the original salts. To get higher percentages of CH cost more than it is worth so they stop the process at an economical level, it gets the pool shock job done but isn’t crazy expensive. He did not have a suggestion for long term storage. They sell it in plastic bags that are not gas tight for Chlorine gas. The stores that store / sell volumes of CH have better than average ventilation.

  8. Don’t sniff directly from the jug! You can burn your nose that way.
    In high school chemistry they showed to waft your hand across the opening toward your nose and sniff carefully.

  9. We live on a property that has a 500 gallon, galvanized water storage tank. Is there any issue with using the pool shock with this tank?

    • I’ve read on other sites that you don’t want to mix this together in a metal container. Acid resistant plastic only. You can reuse your old bleach bottles for example.

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